“…As the literature on the subject witnessed a massive growth, we refrain from overviewing it here, redirecting e.g. to [1,3,[9][10][11][12][13][14][15][16]21,26,29,32,33,[38][39][40] for some of the most recent developments and to the reviews [2,34] for more comprehensive discussions. Within the whole theory, prominent efforts have been devoted to the analysis of existence of positive standing wave solutions, with a particular focus on ground states.…”